Granulomatous hypophysitis caused by Rathke's cleft cyst mimicking a growth hormone-secreting pituitary adenoma

We report a case of granulomatous hypophysitis caused by Rathke's cleft cyst (RCC) mimicking a growth hormone (GH)-secreting pituitary adenoma. Neuroradiological and endocrinological evaluations showed abnormal findings consistent with acromegaly: Magnetic resonance imaging demonstrated a pituitary mass lesion, and GH and insulin-like growth factor I levels were markedly elevated, and GH levels were not suppressed in oral glucose tolerance test. Transsphenoidal surgery was performed, but no adenomatous tissue could be detected. Histological examination revealed RCC and concurrent granulomatous giant cell inflammatory reaction of the anterior hypophysis. To the authors’ knowledge, this is the first documented case of granulomatous hypophysitis caused by RCC mimicking a GH-secreting pituitary adenoma.